This invention relates in general to the method of treating waste gases and in particular to a new and useful method for removing noxious components from waste gases.
The starting prior art is such as disclosed, for example, in German OS No. 23 23 508 for scrubbing sulfur dioxide, hydrochloric acid, fluorine, dust, and similar contaminents from flue gases. Even though not disclosed expressly, this prior art is obviously connected to a substantial reduction of noxious matter emissions in large firing installations, to obtain at the same time clean, usable, and thus marketable separation products, particularly gypsum.
The waste gas decontamination is important also to other industrial branches; in this connection, it may be that the utilization of the obtained separation products will appear far less important than the purpose proper, namely the decontamination.
In chemical processes, particularly also in the manufacture of semiconductors, poisonous, combustible and/or explosive gases are employed as starting products, or they form undesirable byproducts. This primarily includes gases of the group of covalent hydrides. Considerable problems are further encountered with the removal from waste gases of undecomposed trialkyl phosphanes insoluble in water.
In industrial gas separation plants provided to this end, the waste gases to be decontaminated are either burned, or directed through active carbon filters, or chemically converted. A combustion of inflammable and toxic gases or vapors is suitable particularly for unreactive organic compounds and for the removal of noxious substances containing certain metals, phosphorous or sulfur, and whose numerous compounds are toxic, corrosive, or otherwise noxious to the environment. This is done, for example, by means of a primary hydrogen flame with a considerable excess of oxygen in a coolable, closed combustion space specifically designed for this purpose. (see enclosed prospectus of the company Heraeus Quarzschmelze GmbH "Combustion Apparatus HI").
What is critical in that method is an open flame in laboratories where hydrogen is used as a carrier gas. The required large hydrogen amount causes considerable expenses. Toxic residues, such as arsenic oxide, even if diluted, pass into waste water.
Active carbon filters may be employed in instances where the noxious matter can be well handled, as to its kind and amount. It is uneconomical if such filters must be exchanged after short periods of time, and critical or even prohibitive, if changes must be made at unpredictable points of time.
Cleaning and reuse are problematic in view of the toxic adsorption products, so that relatively large volumina must be disposed of as extra waste.
A chemical conversion, such as described in the periodical Chemie-Technik, Vol. 11, 1982, No. 1, Pages 55,56 by means of copper sulfate and sulfuric acid, may be suitable for covalent hydrides. Problems arise, however, with element-organic compounds. For example, trimethylphosphine is converted to phosphonium salts, which, in non-acid environment, are reconverted into the initial product. The necessary admixture of fresh air upstream of the adsorption plant may result in uncontrollable reactions of compounds sensitive to air, such as trimethylindium in CVD plants.